The present disclosure relates generally to an electrostatographic or xerographic printing machine, and more particularly concerns a fixing device and a fixing method of forming an unfixed toner image of an image pattern corresponding to objective image information on a surface of a recording media.
In a typical electrostatographic reproduction process machine, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is imagewise exposed in order to selectively dissipate charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated at a thermal fusing apparatus at a desired operating temperature so as to fuse and permanently affix the powder image to the copy sheet having a certain gloss. In recent years, in particular, for a full-color image, a demand for an enhancement of image quality by making the image glossy has been increased. It is highly desirable to have printed images with uniform gloss throughout the entire sheet.
Fuser gaps exist between consecutive sheets of paper (inter-document zone or IDZ). Applicants have found in a print job consisting of many sheets of paper, if the fusers are asynchronous with the page stream, IDZs create hot zones on the fuser which come around and create high temperature zones within the sheets of paper that come in contact with them. These step changes in the paper temperature and previously fused image contact with the fusers can lead to gloss variations (gloss non-uniformity) that are very obvious to the human eye due to the abrupt nature of the temperature change in the process direction. A conventional solution to this problem is to operate only at fuser temperatures where gloss is independent of temperature. This is not feasible when a lower gloss level is desired.
It is desirable to have a simple apparatus construction which can generate images with high glossiness and is free from gloss non-uniformity.